As a skilled artisan may appreciate, fluid machines such as pumps, which operate over a wide range of capacities, are subjected to cavitation surges at low flow rates and at moderate to low values of Net Positive Suction Head (NPSH). A flow rate of less than about 50% of the pump's design flow rate may be considered a low flow rate. Moderate to low values of Net Positive Suction Head (NPSH) are generally those that produce a pump pressure rise reduction of 1% to 3% below the pressure rise obtained in the absence of NPSH influence.
When cavitation and recirculation exist simultaneously, cavitation in the pump suction or intake can, and often does, surge far upstream. Such surges often create vibrations characterized by low frequency shuttling. These vibrations, in turn, may cause numerous mechanical problems, i.e., bearing failure, seal failure, and etc. As is evidenced from the art, several attempts at reducing pump cavitation have been made.
U.S. Pat. Nos. 3,504,986; 4,375,937; and, 4,375,938 disclose various pump housings having fluidic passageways provided therein for capturing recirculating fluids in a manner reducing pump cavitation surge.
U.S. Pat. Nos. 3,384,022; 3,664,759; 4,150,916; and, 4,239,453 disclose pumps having various restriction means disposed within the pump inlet passageway for redirecting backflowing fluids in a manner reducing pump cavitation surge.